Evaluation of GIC Thermal Capability of Power Transformers - Part II: Shell Form Transformers

Abstract

As stated in Part I of this paper, this Part II of the paper deals with evaluation of GIC Thermal Capability of Shell form Transformers. This evaluation is based on thermal impact of GIC on the transformer tank because, in these transformers, the tank is the structural part that experiences the highest temperature increase when the transformer is subjected to GIC. Again, in this part of the paper, it is demonstrated that the GIC Thermal Capability of a transformer is an even stronger function of the design of that transformer, especially the winding arrangements used in the design. This is because heating of the tank under GIC is caused by a combination of both the AC leakage flux and the DC flux that impinge on the tank when the core is saturated due to GIC. It was found that the GIC Thermal Capability of some Shell form transformer designs can be considerably low and that it is not practical to decide on a GIC limiting criteria for Shell form transformers unless detailed magnetic and thermal design modeling is performed. Additionally, the paper presents impact of Load and duration of GIC pulses on the GIC Thermal Capability of Shell form transformers.